Lactation Notes

Review Session & Lecture Exam Updates

  • Review PowerPoint from the review session is available on Canvas.
  • Lab Final:
    • Worth 50 points.
  • Lecture Exams:
    • Scores to be posted over the weekend.
    • Exams taken a week later will also be graded.

Lactation

  • Overview:
    • Covers the final stage of animal development: providing nutrition to offspring.
    • Includes mammals in general.
  • Topics:
    • Milk composition and synthesis.
    • Mammary gland development.
    • Physiology of lactation.

What Defines a Mammal?

  • Two defining characteristics:
    • Hair.
    • Mammary glands.
  • Importance of mammary glands:
    • Newborn mammals are primitive and helpless.
    • Require nutrition from milk to grow and develop.
  • Other Animals:
    • Reptiles and birds provide nutrition via yolk.

Hairless Animals

  • Breeds of hairless animals exist due to mutations.
  • Normally, these animals would have hair and be classified as mammals.
  • Genetic "freaks" without hair are still classified as mammals due to the potential for hair production.

Mammalian Evolution

  • Evolved about 200 million years ago from small, rodent-like animals.
  • Over 5,000 species of mammals exist today.

Examples of Mammals

  • Mammals are defined by milk production and hair.
    • Echidna (Spiny Anteater):
      • Australian animal (genus Tachyglossus).
      • One of the egg-laying mammals (monotremes).
    • Duck-billed Platypus:
      • Defined as a mammal due to milk and hair.
      • Monotreme.

Monotremes (Protheria)

  • Egg-laying mammals.
  • Do not have placentas (eggs provide early nutrition).
  • Produce milk for nutrition.
  • Limited to Australia and New Guinea.
  • Early, dead-end branch of ancestral mammals.
  • Primitive mammary glands without nipples.
  • Secrete milk from ducts in the skin (similar to sweat glands).
    • Duck-billed platypuses secrete milk onto stiff mammary hairs.
    • Echidnas secrete milk into a pouch.

Marsupials (Metatheria)

  • Possess teats and more developed mammary glands than monotremes.
  • Often referred to as mammals giving premature birth.
  • Newborns (joeys) are delivered prematurely.
  • Joeys crawl to find a teat to latch onto for nutrition.

Marsupial Development

  • Newborn Tamar Wallaby (70 days old):
    • Blind, no fur.
    • Size of a jelly bean.
  • Wallaby Joey (150 days old):
    • Still small.
  • Joey (200 days old):
    • Has fur, eyes open, more independent.
  • Newborn opossums are also very small.

Placental Mammals (Eutheria)

  • Have fully developed placentas.
  • Young are born more mature.
  • Receive nutrition from lactation.
  • More complex placenta than marsupials.

Fetal Dependency in Eutherians

  • Fetus depends on the mother for:
    • Temperature.
    • Moisture.
    • Sterile environment.
  • Fetus grows rapidly in utero due to placental nutrition.

Newborn Immaturity

  • Newborns are relatively immature:
    • Soft bones.
    • Immature digestive tract and metabolic system (cannot consume solid food).
    • Immature immune system.
  • Newborns are altricial (born in an immature state).
  • Require nourishment and depend on the mother.
  • Human babies considered more altricial than foals.

Milk as a Source of Nutrients

  • Milk provides:
    • Nutrients for growth.
    • Protective factors like antibodies (to combat immature immune system).
    • Growth factors (to mature the gut and digestive system).
  • Neonate changes rapidly in early life.
  • Early nutrition from the mother is critical for development.

Trick Question: Which Animal Produces Milk?

  • Pigeons.
    • Produce "crop milk".
    • Crop milk is made of sloughed cells from the crop.
    • Regurgitated to newborns.
    • Controlled by prolactin.
    • Not technically milk, but called crop milk due to its function.
  • Prolactin:
    • Important for mammary gland development.
    • Important for maternal behavior, especially in birds.

Dairy Animals

  • Animals that provide products for human consumption.
  • Dairy cows provide milk for cheese, milk, ice cream, etc.

High Milk Production Example

  • Dairy cow producing almost 45,000 pounds of milk in 365 days.
  • 5.6% fat, 2,000 pounds of butterfat, 1,200 pounds of protein.
  • Translates to about 5,600 gallons of milk in one year.
  • Requires about 2.5 million gallons of blood through the udder each year.

Variety of Dairy Animals

  • Different cultures use milk from various animals:
    • Goats, sheep, water buffaloes, camels, yaks, mares.
  • Often, the baby nurses first to stimulate milk let-down; then, the milk is hand-milked.

Camel's Milk

  • Question about water content in camel's milk due to desert environment.

Cow's Milk Composition

  • Main component: Water.
  • Lactose (disaccharide of glucose and galactose).
  • Lipids.
  • Proteins.
  • Minerals (e.g., Calcium).
  • Vitamins (fortified with Vitamin D).
  • Other components.

Review Questions

  • What animals lactate? Mammals.
  • What produces milk? Mammary glands.
  • What is produced? Milk.
  • Where does it happen? Ventral area.
  • When does it happen? After birth.
  • Why does it happen? Nutrition for neonate.
  • How does it happen? Complex process (to be discussed).

Milk Properties

  • Biochemical and physicochemical properties.
  • Synthesis of milk.
  • Importance to nursing young and humans.
  • Factors affecting milk component concentration.

Milk Structure

  • Milk at low magnification:
    • Fat globules (yellow).
    • Plasma phase (skim milk).
    • Emulsion (fat globules emulsified in skim milk).
    • Fat globules stay in solution due to plasma membrane coating.
  • Milk is a suspension of immune cells and epithelial cells.
  • Milk is a colloid due to casein micelles in the serum (white protein).
  • Water-soluble components: milk sugar, minerals, whey proteins (solution).

Emulsion of Fat Globules

  • Emulsion: liquid dispersed in an immiscible liquid.
  • Fat globules are dispersed in the water-based aqueous phase.
  • Separation occurs over time (cream rises to the top).
  • Homogenization breaks down large fat globules into smaller ones for a more stable emulsion.

Milk as a Colloid

  • Casein micelles (small micelles in the liquid) require an electron microscope to observe.
  • Disrupting the colloid structure (using renin or pH) makes cheese.
  • Casein precipitates, forming cheese curds.

Casein Micelle Structure

  • Made of many small submicelles.
  • Primarily casein (major protein in milk).
  • Calcium phosphate mixed in (for calcium stability and bioavailability).

Composition Variability

  • Milk composition is not constant.
  • Depends on:
    • Species.
    • Strain/breed.
    • Stage of lactation.
  • Milk fat is the most variable non-mineral component.
  • Lactose is the least variable component.

Species Variability in Milk Fat

  • Cow's milk: ~3.5% fat.
  • Human milk: slightly higher.
  • Seal milk: very high (similar to cream cheese).

Milk Fat Breed Variability

  • Jerseys: high fat (~5%).
  • Brown Swiss: less fat.
  • Holsteins: even less fat.
  • Water buffalo: more fat.
  • Zebu: higher fat than typical dairy cows.

Stage of Lactation

  • Influences milk components.
  • Important for newborn's nutritional requirements.
  • Early lactation (after calving): high in total protein (almost 20%).
  • Casein and whey protein also high.
  • High protein concentration critical due to immunoglobulins in colostrum.

Immunoglobulins (Antibodies)

  • Found in body fluids.
  • Neutralize pathogens (bind to bacteria, viruses, etc.).
  • Newborns often have few antibodies.
  • Cows: antibodies not transported across the placenta.
  • Fetuses get antibodies from colostrum.
  • Even in humans (with placental transfer), colostrum supplements antibody levels.

Immunoglobulin Levels in Newborn Calves

  • Calves not receiving colostrum: low immunoglobulin levels.
  • Calves receiving colostrum: much higher levels.
  • Colostrum should be fed within a couple of hours of birth.
  • Gut closes after a day or two, preventing antibody absorption.
  • Provides passive immunity.

Types of Immunity Review

  • Adaptive immunity: requires time and antibodies.
  • Innate immunity: broad, general immunity.
  • Adaptive immunity:
    • Natural: infection or maternal antibodies.
    • Artificial:
      • Active: immunization.
      • Passive: consuming antibodies (colostrum).

Cow Anatomy

  • Udder: entire structure including mammary glands and teats.
  • Dairy cows typically have four mammary glands and four teats.
  • Mammary glands are skin glands.
  • Large arteries and veins go through the inguinal canal.
  • Udder divided into two halves by the median suspensory ligament.
  • Fore and rear quarters are separated by connective tissue, but have no ligament support.

Udder Support

  • Median suspensory ligament divides the udder and attaches to the body wall.
  • Lateral suspensory ligaments provide less support and attach to tendons that attach to the pelvis.
  • Skin provides very little support.
  • Breakdown of median suspensory ligament causes udder floor to drop and teats to point outward.